[Wien] Charged cell versus virtual atom?

[Laurence Marks]

To clarify first: Nb-doped STO is commercial, with Nb on the Ti site doping
the STO n-type -- Nb is 5+ valence versus 4+ for Ti. It is known that the
carriers are delocalized.

I am interested in the near-surface band bending, both clean and with a
Shottky contact to Pt/Pd under force. This models some of the terms in the
trbolectricity of a moving Shottky diode contact. (This is bare-bones
details.)

Band bending, but also energy (to get contact forces and bulk lattice)
matter.

While having Z=22.0675 is more like V doped, it does balance the charge.
Charged cells have approximations for the total energy, and add a
background potential, which raises issues in my mind for the vacuum & Pd/Pt.

Simple approximations have ~80 total atoms, 25 unique; a more complete has
~700/190 for total/unique.

To zero'th order the two look similar, but.....

--
Professor Laurence Marks
Department of Materials Science and Engineering, Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi

On Mon, May 2, 2022, 5:41 AM Fecher, Gerhard <fecher at uni-mainz.de> wrote:

> Z=40.0625 means you replace all Ti by Zr + a little electrons, instead of
> Ti + 1/16 e-, isn't it ?
> I assume that changing the charge by epsilon e- works only for
> neighbouring elements, on top,  if you rplace the Z of Ti (22) by 22+1=23
> then you have fully V and not Ti+1/2 Cr, etc..
>
> ==> supercell even if its vast     (or some program that uses CPA to have
> a mean field behaviour).
>
> Ciao
> Gerhard
>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
>
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Physics
> Johannes Gutenberg - University
> 55099 Mainz
> ________________________________________
> Von: Wien [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Rubel,
> Oleg [rubelo at mcmaster.ca]
> Gesendet: Montag, 2. Mai 2022 05:19
> An: A Mailing list for WIEN2k users
> Betreff: Re: [Wien] Charged cell versus virtual atom?
>
> I must admit that I do not have any experience with the fractional Z, but
> it seems that the option (b) could be better. At least it has some chemical
> specificity. Maybe it is better to use Z=40.0625 to differentiate between
> Nb and V?
>
> Best regards
> Oleg
>
> ________________________________________
> From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of
> Laurence Marks <laurence.marks at gmail.com>
> Sent: Sunday, May 1, 2022 16:59
> To: A Mailing list for WIEN2k users
> Subject: [Wien] Charged cell versus virtual atom?
>
> As part of a larger problem, I need to simulate a Nb-doped SrTiO3 surface,
> where 1/16 Ti sites is Nb. To first order this is 1/16 extra electrons.
> There are two ways I can think of to do this:
> a) Charged cell calculation, with extra electrons + background charge.
> b) Virtual atom, where the Ti's have a Z of 22.0625.
>
> Does anyone have any experience with something similar? I can think of
> reasons why both have issues, e.g. the extra potential in the vacuum in a).
>
> N.B., doing a super-duper surface cell with 1/16 Ti changed is too vast.
>
> --
> Professor Laurence Marks
> Department of Materials Science and Engineering
> Northwestern University
> http://www.numis.northwestern.edu<http://www.numis.northwestern.edu>
> "Research is to see what everybody else has seen, and to think what nobody
> else has thought", Albert Szent-Györgyi
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